1. Field of the Invention
This invention relates to an organosiloxane polymer suitable for use as a base polymer in photo-curable resin compositions, a photo-curable resin composition comprising the same, a patterning process, and a substrate protective film made from the composition.
2. Background Art
Organosiloxane base photo-curable resin compositions are advantageously used as protective coatings, insulating coatings and release coatings and even as photoresists for fine-circuitry fabrication.
Among prior art organosiloxane base photo-curable resin compositions, those using photoacid generators are well known. For example, JP-A 55-105627 describes a resin composition comprising an epoxy radical-containing organosiloxane and a diaryl iodonium salt as the photoacid generator. JP-A 59-500522 describes a resin composition comprising a vinyl ether radical-containing organosiloxane and an onium salt as the photoacid generator. These resin compositions, however, suffer from the problems that only photoacid generators of selected type can be used because of the incompatibility between the resin and the photoacid generator, and only light sources in a limited range of wavelength can be utilized. If these resin compositions are used as resist materials for micro-fabrication, the resins are insufficiently photo-curable to achieve precise micro-patterning. Also, an organosiloxane base photo-curable resin composition using a linear hydroxyorganosiloxane is known in the art as disclosed in JP-A 11-335464, but its strength is not so high. As the resist material for fine-circuitry fabrication, resin compositions comprising a cresol novolac resin or polyhydroxystyrene resin, an alkoxymethylated amino resin and a photoacid generator are known as disclosed in JP-A 4-136860. These materials have the shortcoming that cured films after development are less elastic or less compliant so that when other resins are laminated thereon, delamination or cracking readily occurs due to differential stresses. Because of their essentially low transparency, thick films tend to lose sensitivity. Besides, when such compositions are used as a protective insulating material for substrates, there arises an essential problem: poor adhesion to substrates.
The recent outstanding progress of the information technology encourages the size and weight reduction of electronic parts used in low-profile information terminals as typified by mobile phones, digital cameras and portable audio equipment. To attain such purposes, the concept of wafer-level chip size package (W-CSP) was proposed for the manufacture of semiconductor devices and has been used in practice.
In a general process of the W-CSP, a thin-film seed layer of titanium/copper is disposed on a wafer which has completed a conventional LSI process, a pattern is formed using a thick film of photosensitive material, and copper plating is performed to form redistribution wiring. At this point, the photosensitive material is once removed. On the copper plated redistribution wiring and copper thin-film seed layer having a step therebetween, a pattern is formed using a thick film of photosensitive material again. Copper plating is performed again to form via posts.
As is well known in the art, the metal of copper tends to readily bond with air-borne oxygen to form an oxide film and also tends to allow copper atoms to gradually diffuse into an organic material disposed in close contact therewith, and is chemically highly active. Thus, when a photosensitive material is imagewise processed on the copper surface, difficulties often arise which are not encountered in the processing on films of other metals or oxides or nitrides thereof. In the above-described proposal, patterning on the copper surface is unstable, imposing difficulty in finding a compromise between resolution and close adhesion. This raises the problem that the coating of the composition separates away from the substrate during development or is left in unexposed areas even after development. It would be desirable to solve these problems.